I'm thinking to buy the filter for outside shooting which will include some nature(landscape) but mostly portraits during sunny days.
I have seen that there are following filters:
UV
polarization
SKYlight
Can you explane the use of these filters and suggest what is the best buy.
Also how the snow and sunlight are connected to these filters.
Thanks

If you are shooting digital, you don't need a UV filter - most UV filters sold today are attached to protect the surface of the front element of the lens against scratches. Don't use a Skylight filter on digital - it distorts the colours.

If you are shooting film, you can use a UV or Skylight filter to block UV from the film - it can cause minor discolouration.

A polarising filter is a different animal. It's mainly used to block glare (on water, especially), and to darken the sky so it's blue, not white. You can use a polarising filter (usually circular pol) on digital or film.

That's the short version. For more info, I refer you to our good friend Google.

__________________they say you have to take a thousand bad photos before you can take a good one - I have mastered the bad photos part...

If you're in the market for filters you might want to consider a 2X or 3X Neutral Density filter - especially if you are shooting digital. Digital has inherently more DOF than film and sometimes in bright daylight it's hard to throw the background out of focus as much as you might like. The polarizing filter can give you the same effect (to a point) if you are using it anyway - but if you don't want/need the polarizer it'll cut your post processing time to use the ND.

For landscape work you might want to cosider a 2 or 3 stop Graduated Netral density filter in either a hard or soft step depending on your application. The diference between a hard and soft step is the transition. Hard step is fairly abrupt but is great any place where you have a very distinct transition such as a sunset or sunrise at the beach. The soft step with the softer transition would be better where you do not have a distinct transition.
If going with Graduated ND filters I personally would look at Singh Ray or Lee rather than buying round GND filters in rings. With the GND mounted in a ring the transition is smack in the middle which can limit its effectiveness, unless your transitions is in the middle of your composition. The larger Sing Ray filters allow me to place the transition pretty much where I want it. I just hold it against the front of the lens and adjust it to the position I desire.
Image below was with the Singh Ray 3 stop Hard Edge GND
Regards,
John

If you've got expensive lenes then get good coated UV filters to simply
protect the lenes against damage. If you don't get good ones they will
cause the the lenses to flare much more easily (sabotaging the quality
of the lenses you use.) In addition, even with a good coated UV filter
if you are shooting into the sun it is often best to remove the filter.

By the way, digital cameras really do need a UV filter so they are all
designed to include an internal one.